The present invention relates to an impact serial printer of the type which prints by impacting a record medium with type elements.
Recently, in the field of printers, personal and hand held printers suitable for use in printing desk-top electronic calculators and the like have come into increasing use, particularly such printers of a reduced size and weight. As the printer for such calculators, the so-called impact type serial printer has become favored partly because of the clearness of the printed data and partly because the printer may be easily used with ordinary paper. This type of printer, although the size and weight are reduced advantageously, is inferior to conventional large-sized printers in regard to the variety of data that may be printed, because there is a practical limit in the number of type elements that can be formed on the type wheel typically used with such printers.
In order to obviate this shortcoming, U.S. Pat. No. 4,051,942 proposes an improved small-sized serial printer having two type wheels. One of these type wheels is shiftable in the direction of a line to be printed, while the other prints only at the rightmost column position so that printing is conducted by selectively using these two type wheels.
The serial printer disclosed in the above-mentioned patent can have a small size and comparatively simple construction because only one type wheel need to be shiftable along the entire line of printing. However, there still is a limit in the number of type elements because, in order to maintain the small size of the printer as a whole, the outside diameter of the type wheel cannot be increased sufficiently to enable a large number of type elements to be placed around its periphery. For the same reason, this serial printer cannot suitably be used for two-color printing.